This invention is concerned with catechol-aldehyde condensation products and their application in adhering polymers to reinforcing fabrics and cords. The commonly used cord-to-rubber adhesives are water dispersions of latex and resorcinol-formaldehyde resins with other ingredients such as carbon black and blocked polyisocyanates added for specific end results. The composition and process disclosed herein have substituted catechol-formaldehyde resins for part or all of the resorcinol-formaldehyde resin.
The weaving, dipping, heat setting, and calendering of reinforcing fabric is explained in the Kirk-Othmer Encyclopedia of Chemical Technology, 2nd ed., Vol. 20, p. 334, (John Wiley & Sons, New York, 1969) which is incorporated by reference into this specification. Adhesive formulations are only one part of the complex technology of fabric processing.
Resorcinol-formaldehyde latex adhesives for adhering reinforcing fabric to rubber have been known and used for years. They are the subject of many patents which cover variations in latices used, modifications of the resin, and additional ingredients for resistance to heat degradation, stronger bond, or other beneficial effects.
Polyhydroxy and dihydroxy phenols in general have been disclosed and claimed in several of the prior art patents and in the literature. U.S. Pat. No. 2,128,635 discloses and claims the application to fabric of dihydric and polyhydric phenol-aldehyde condensation products mixed with rubber latex for bonding the fabric to rubber. This was one of the earliest cord dip adhesives for rayon cord.
Blends of vinylpyridine/diene hydrocarbon latices with polyhydric phenol-aldehyde heat convertible resol are described and claimed in U.S. Pat. No. Re. 23,451. These are the first successful adhesives developed for use on nylon tire cord. Catechol is mentioned as an example of a suitable polyhydric phenol.
An improvement on the vinylpyridine/diene type adhesives is revealed in U.S. Pat. No. 3,194,294 which teaches the stabilization of these dip solutions by incorporating a methylol-containing formaldehyde donor and ammonia into the mixture. Although dihydroxy and polyhydroxy phenols are said to be suitable, those with hydroxy groups meta to each other are specifically mentioned as substitutes for resorcinol (column 5, line 46), which would exclude catechol.
Dihydric or polyhydric phenolic resins are also either disclosed or claimed in two Canadian Patents, Nos. 834,806 (corresponds to U.S. Pat. No. 3,437,122) and 984,076.
In all of the prior art patents disclosing or claiming dihydric or polyhydric phenolic resins listed above, the great majority of the working examples utilize resorcinol-formaldehyde resins and none of the examples utilize catechol-formaldehyde resins. In fact, of the three dihydric phenols (resorcinol, catechol, and hydroquinone) only resorcinol is commercially important in adhesive resin manufacture. Although catechol undergoes many of the typical reactions of phenols, in most of them it is considerably less reactive than resorcinol.
The condensation of aldehydes such as formaldehyde and acetaldehyde with catechol leads to methylenedipyrocatechol compounds and higher molecular weight condensates. Such a reaction with formaldehyde is described in Chemical Abstracts 54:3287b, which teaches heating the reactants at a pH of 10 for satisfactory results. This type of reaction is used in latex to strengthen molded products as taught by U.S.S.R. Pat. No. 168,413 (C.A. 63:P775a). Catechol-formaldehyde resin is used in a process for treating papermaker's felt in U.S. Pat. No. 3,386,849.
Catechol-formaldehyde condensation products have also been utilized in the stabilization of nylon against ultraviolet light and oxidation (U.S. Pat. No. 2,388,676 and Japanese Pat. No. 2,187 issued Mar. 28, 1961).